Untangling the Web from DNS

Michael Walfish Hari Balakrishnan

Massachusetts Institute of Technology

Scott Shenker UC Berkeley/ICSI

IRIS Project

30 March 2004

Introduction

• The Web depends on linking; links contain references

• Properties of DNS-based references encode administrative domain human-friendly

<A HREF=http://domain_name/path_name>click here</A>

• These properties are problems!

Web Links Should Use Flat Identifiers

<A HREF=http://isp.com/dog.jpg>my friend’s dog</A>

<A HREF=http://isp.com/dog.jpg>my friend’s dog</A>

<A HREF=http://f0120123112/ >my friend’s dog</A>

<A HREF=http://f0120123112/ >my friend’s dog</A>

Current Proposed

• This talk: That we should build

this That we can build this

Outline

I. Argue for flat tags instead of DNS-based URLs

II. Resolution service for flat tags

Status Quo

DNS

IP addr

a.comBrowser

HTTP GET: /dog.jpg

http://http://<A HREF=

http://a.com/

dog.jpg>Spot</A>

<A HREF=

http://a.com/

dog.jpg>Spot</A>

Web Page

Why not DNS?

“Reference Resolution Service”

Goal #1: Stable References

Stable=“reference is invariant when object moves”

• In other words, links shouldn’t break• DNS-based URLs are not stable . . .

Object Movement Breaks Links

isp.com

“dog.jpg”

isp-2.com

“spot.jpg”

“HTTP 404”

HTTP GET:/dog.jpg

Browser

http://http://<A HREF=

http://isp.com/dog.jpg>Spot</A>

<A HREF=

http://isp.com/dog.jpg>Spot</A>

URLs hard-code a domain and a path

Object Movement Breaks Links, Cont’d

isp.com

“dog.jpg”

isp-2.com

“spot.jpg”

“HTTP 404”

HTTP GET:/dog.jpg

Browser

http://http://<A HREF=http://isp.com/dog.jpg>Spot</A>

<A HREF=http://isp.com/dog.jpg>Spot</A>

Today’s solutions not stable:• HTTP redirects

need cooperation of original host• Vanity domains, e.g.: internetjoe.org

now owner can’t change

Goal #2: Supporting Object Replication

• Host replication relatively easy today• But per-object replication requires:

separate DNS name for each object virtual hosting so replica servers recognize names configuring DNS to refer to replica servers

isp.com

“/docs/foo.ps”

mit.edu

“~joe/foo.ps”

http://object26.org

HTTP “GET /”

host: object26.org

HTTP “GET /”host: object26.org

What Should References Encode?

• Observe: if the object is allowed to change administrative domains, then the reference can’t encode an administrative domain

• What can the reference encode? Nothing about the object that might change! Especially not the object’s whereabouts!

• What kind of namespace should we use?

Goal #3: Automate Namespace Management

• Automated management implies no fighting over references

• DNS-based URLs do not satisfy this . . .

DNS is a Locus of Contention

• Used as a branding mechanism tremendous legal combat “name squatting”, “typo squatting”,

“reverse hijacking”, . . .

• ICANN and WIPO politics technical coordinator inventing naming

rights set-asides for misspelled trademarks

• Humans will always fight over names . . .

Separate References and User-level Handles

• “So aren’t you just moving the problem?” Yes. But.

Let people fight over handles, not references

Object Location

Human-unfriendly References

User Handles(AOL Keywords,

New Services, etc.)

tussle space[Clark et al., 2002]

Two Principles for References

1. References should not embed object or location semantics

2. References should be human-unfriendly

Flat tags

Minimal interfaceNatural choice:

Outline

I. Argue for flat tags instead of DNS-based URLs

II. Resolution service for flat tags: SFR

Object Location

Flat TagUser Handle

(AOL Keyword,New Handle, etc.)

<A HREF=http://f012c1d/ >Spot</A>

<A HREF=http://f012c1d/ >Spot</A>

Managed DHT-based

Infrastructure

GET(0xf012c1d)

(10.1.2.3, 80, /pics/dog.gif)

o-record

HTTP GET: /pics/dog.gif 10.1.2.3

Web Server

/pics/dog.gif

SFR in a Nutshell

orecAPI• orec = get(tag);• put(tag, orec);Anyone can put() or get()

Resilient Linking

SFR

<A HREF=http://f012012/pub.pdf>here is a paper</A>

<A HREF=http://f012012/pub.pdf>here is a paper</A>

HTTP GET:

/docs/pub.pdf

10.1.2.3

/docs/

20.2.4.6

HTTP GET:

/~user/pubs/pub.pdf(10.1.2.3,80,/docs/)(20.2.4.6,80,

/~user/pubs/)/~user/pubs/

• tag abstracts all object reachability information• objects: any granularity (files, directories, hosts)

(Doesn’t address massive replication)

Flexible Object Replication

(IP1, port1, path1),(IP2, port2, path2),(IP3, port3, path3),. . .

0xf012012SFR

o-record

• Grass-roots Replication People replicate each other’s content Does not require control over Web servers

Reference Management

• Requirements No collisions, even under network partition References must be human-unfriendly Only authorized updates to o-records

• Approach: randomness and self-certification tag = hash(pubkey, salt) o-record has pubkey, salt, signature anyone can check if tag and o-record match

Latency

• Problem: Lookups should be fast

• Solution: lots of TTL-based caching Clients and DHT nodes cache o-records DHT nodes cache each other’s locations

In Chord, aggressive location caching 2 or 3 hops per lookup

Could also use “one-hop” or Beehive

Outline

I. Argue for flat tags instead of DNS-based URLs

II. Resolution service for flat tags: SFR

III. Related Work / Summary / Conclusion

Related Work

• URN (Universal Resource Name) DOI: an existing URN implementation

• PURL (Permanent URL)• Globe• Open Network Handles• DNS over Chord

Summary

• Should we build flat references for the Web? Yes!

• Can we build flat references for the Web? Yes! (Our implementation is usable.)

• Lots of future work . . .

Conclusion

• DNS-based URLs certainly convenient!

• But flat tags better for linking

• Future: type DNS names, link with flat tags?

Appendix Slides

Implementation

http://http:// HTTPSFR Web

Proxy

SFR Client

SFR Portal

Chord

DHash

SFR Server

Web Client

• Proxy allows: End-users to experience SFR

latency Dynamic population of SFR

infrastructure with o-records

orec = get(tag)put(orec,tag)

HTTP

SFR Portal

GetRequestGetResponse

PlanetLab

Evaluation

SFR data ——— • eight day trace• 390 virtual hosts; 130

nodes in Chord ring on PlanetLab

• latency seen by SFR portal• most queries are two hops• informal feedback:

generally indistinguishable from DNS

Comparison meant to be suggestive not conclusive

DNS data ——— ——— • collected at MIT CSAIL, Feb. 2004

SFR ComponentsPortal

Portal

Relay

Relay

Relay

OrgStore

SFRInfrastructure

Organization

• Infrastructure stores (tag, o-record) pairs• Caching throughout; o-record has TTL field

SFR Client

ApplicationSFR Client

ApplicationSFR Client

Application

SFR Client

Application

Portal

Portal

Relay

Relay

Relay

OrgStore

SFRInfrastructure

Organization

Fate Sharing

put(tag,orec)

get(tag)

• Fate sharing via write-localitySimple case . . .

SFR Client

ApplicationSFR Client

ApplicationSFR Client

Application

SFR Client

Application

Alternate SFR Design: SFR--

• SFR stores only pointers to organizations• Analogous to NS records in DNS

GET(0xf012120)

org ptr: x

User

SFRInfrastructure

x

GET(0xf012120)

meta-data (IP addr, etc.)

Organization

When Files Separate From Directories

SFR

<A HREF=http://f012012/pub3.ps>here is a paper</A>

<A HREF=http://f012012/pub3.ps>here is a paper</A>

HTTP GET:

/doc/pub3.ps

10.1.2.3

/doc/pub1.ps

20.2.4.6HTTP GET:

/abc/pub3.

ps

(10.1.2.3,80,/doc/)

redirect ptr:x

/abc/pub3.ps

/doc/pub2.ps

/doc/pub3.psx

GET(0xf012012)

Location Caching

• Simulate effect of location caching 20 lookups/sec; one failure and one birth per

10 sec. Timeout rate: 4% 1000 nodes